Implantable or insertable medical devices for controlled delivery of a therapeutic agent

ABSTRACT

The present invention is directed to novel implantable or insertable medical devices that provide controlled release of a therapeutic agent. According to an embodiment of the present invention, a therapeutic-agent-releasing medical device is provided, which comprises: (a) an implantable or insertable medical device; (b) a release layer disposed over at least a portion of the implantable or insertable medical device; and (c) a therapeutic agent. The release layer comprises a styrene copolymer and at least one additional polymer. The release layer regulates the rate of release of the therapeutic agent from the medical device upon implantation or insertion of the device into a patient. The present invention is also directed to methods of forming the above implantable or insertable medical devices, methods of administering a therapeutic agent to a patient using such devices, and methods of modulating the release of therapeutic agent from such devices.

STATEMENT OF RELATED APPLICATIONS

This is a continuation of U.S. patent application Ser. No. 10/175,334,filed Jun. 19, 2002 now U.S. Pat. No. 7,105,175, entitled “Implantableof Insertable Medical Devices For Controlled Delivery Of TherapeuticAgent,” which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to implantable or insertable medicaldevices for controlled delivery of one or more therapeutic agents.

BACKGROUND OF THE INVENTION

Numerous medical devices have been developed for the delivery oftherapeutic agents to the body.

In accordance with some delivery strategies, a therapeutic agent isprovided within a polymeric carrier layer and/or (b) beneath a polymericbarrier layer that is associated with an implantable or insertablemedical device. Once the medical device is placed at the desiredlocation within a patient, the therapeutic agent is released from themedical device at a rate that is dependent upon the nature of thepolymeric carrier and/or barrier layer.

The desired release profile for the therapeutic agent is dependent uponthe particular treatment at hand, including the specific condition beingtreated, the specific therapeutic agent selected, the specific site ofadministration, and so forth. As a result, there is a continuing needfor polymeric layers, including polymeric barrier layers and carrierlayers, that are able to provide a broad range of therapeutic agentrelease rates.

SUMMARY OF THE INVENTION

The present invention is directed to novel implantable or insertablemedical devices, which provide for release of a therapeutic agent.According to a first aspect of the present invention, atherapeutic-agent-releasing medical device is provided, which comprises:(a) an implantable or insertable medical device; (b) a release layerdisposed over at least a portion of the implantable or insertablemedical device; and (c) a therapeutic agent. The release layer comprisesa styrene copolymer and an additional polymer. The release layerregulates the rate of release of the therapeutic agent from the medicaldevice upon implantation or insertion of the device into a patient.Alternating and random styrene copolymers are preferred.

In some embodiments, the release layer is a carrier layer that comprisesthe therapeutic agent. In other embodiments, the release layer is abarrier layer disposed over a therapeutic-agent-containing region, whichcomprises the therapeutic agent.

Preferred medical devices include catheters, guide wires, balloons,filters, stents, stent grafts, vascular grafts, vascular patches,shunts, and intraluminal paving systems. The device can be adapted, forexample, for implantation or insertion into the coronary vasculature,peripheral vascular system, esophagus, trachea, colon, biliary tract,urinary tract, prostate or brain.

Beneficial therapeutic agents for the practice of the present inventioninclude anti-thrombotic agents, anti-proliferative agents,anti-inflammatory agents, anti-migratory agents, agents affectingextracellular matrix production and organization, antineoplastic agents,anti-mitotic agents, anesthetic agents, anti-coagulants, vascular cellgrowth promoters, vascular cell growth inhibitors, cholesterol-loweringagents, vasodilating agents, and agents that interfere with endogenousvasoactive mechanisms.

Preferred styrene copolymers include copolymers comprising (a) a styrenemonomer and (b) a monomer comprising a carbon-carbon double bond.Monomers comprising a carbon-carbon double bond include alkylenemonomers (e.g., ethylene, propylene, butadiene, butylenes, isobutyleneand isoprene), vinyl monomers (e.g., vinyl ethers, vinyl acetates, vinylaliphatics, halogenated vinyl compounds, vinyl pyrrolidone,acrylonitrile, vinyl alcohols, and vinyl acrylamides), acrylate monomersor derivatives of the same (e.g., methyl acrylate, methyl methacrylate,acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethylmethacrylate, glyceryl acrylate, glyceryl methacrylate, acrylamide,methacrylamide and ethacrylamide), and maleic anhydride monomers orderivatives of the same (e.g., maleic anhydride, maleic anhydride in afree acid form, maleic anhydride in a salt form, or maleic anhydride ina partial ester form).

Specific styrene copolymers for the practice of the present inventioninclude copolymers of styrene and maleic anhydride and copolymers ofstyrene and acrylonitrile.

In some embodiments, the additional polymer is blended with the styrenecopolymer in the release layer. In others, the additional polymer iscrosslinked with the styrene copolymer in the release layer. Specificexamples of additional polymers for the practice of the presentinvention include elastomers such as the following: (1) copolymerscontaining (a) one or more blocks of polyisobutylene and (b) one or moreblocks of polystyrene or poly-alpha-methylstyrene, (2) copolymerscontaining (a) one or more blocks of polystyrene orpoly-alpha-methylstyrene and (b) one or more polymer blocks of ethyleneand butylene, and (3) poly(butyl methacrylates).

According to another aspect of the present invention, a method of makinga therapeutic-agent-releasing medical device is provided. The methodcomprises: (a) providing a solution comprising one or more solvents, astyrene copolymer and an additional polymer; (b) applying the solutionto a surface of an implantable or insertable medical device; and (c)removing the solvents from the solution to form a release layer. Solventspraying is a preferred technique for applying the above solution.

In some embodiments, for example, where a carrier layer is being formed,the solution further comprises the therapeutic agent. In otherembodiments, for example, where a barrier layer is being formed, thesolution is applied over a therapeutic-agent-containing region thatcomprises the therapeutic agent.

According to another aspect of the present invention, a method ofmodulating a rate of release of a therapeutic agent from a release layeris provided. The release layer is disposed over at least a portion of animplantable or insertable medical device and comprises a styrenecopolymer and an additional polymer. Release is modulated by changingthe composition of the release layer. In some embodiments, the releaserate can be modulated by changing the amount of the styrene copolymerrelative to the amount of the additional polymer. For example, the rateof release of the therapeutic agent can be increased in certainembodiments by increasing the amount of the styrene copolymer relativeto the amount of the additional polymer, while the rate of release canbe decreased by decreasing the amount of the styrene copolymer relativeto the amount of the additional polymer.

In other embodiments, the release rate is modulated by changing themolecular weight of the styrene copolymer. In still other embodiments,the release rate is modulated by changing the amount of the styrenemonomer relative to the total amount of monomer within the styrenecopolymer.

One advantage of the present invention is that implantable or insertablemedical devices are provided, which provide for controlled release of atherapeutic agent.

Another advantage of the present invention is that implantable orinsertable medical devices are provided, which are able to providetherapeutic agent release over a wide variety of time frames.

Another advantage of the present invention is that effective strategiesare provided for controlling the release profile of a therapeutic agentfrom an implantable or insertable medical device.

These and other embodiments and advantages of the present invention willbecome immediately apparent to those of ordinary skill in the art uponreview of the Detailed Description and Claims to follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates cumulative release of paclitaxel as a function oftime for carrier layers containing paclitaxel and (a) poly(butylmethacrylate) homopolymer, (b) polystyrene-polyisobutylene-polystyreneblock copolymer, (c)polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene block copolymer,(d) poly(butyl methacrylate) homopolymer blended with a random copolymerof styrene and maleic anhydride, (e)polystyrene-polyisobutylene-polystyrene block copolymer blended with arandom copolymer of styrene and maleic anhydride and (f)polystyrene-b-poly(ethylene-r-butylene)-b-polystyrene block copolymerblended with a random copolymer of styrene and maleic anhydride.

FIGS. 2A and 2B illustrate cumulative release of paclitaxel as afunction of time for carrier layers containing paclitaxel and (a) apolystyrene-polyisobutylene-polystyrene block copolymer, (b) a randomcopolymer of styrene and maleic anhydride and (c) apolystyrene-polyisobutylene-polystyrene block copolymer blended withvarious amounts of a random copolymer of styrene and maleic anhydride,in accordance with an embodiment of the present invention.

FIG. 3 illustrates cumulative release of paclitaxel as a function oftime for carrier layers containing paclitaxel and (a) apolystyrene-polyisobutylene-polystyrene block copolymer, and (b) apolystyrene-polyisobutylene-polystyrene block copolymer blended withvarious amounts of styrene-co-acrylonitrile copolymer, in accordancewith an embodiment of the present invention.

FIG. 4 illustrates cumulative release of paclitaxel as a function oftime for carrier layers containing paclitaxel and (a)polystyrene-polyisobutylene-polystyrene block copolymer, (b)polystyrene-polyisobutylene-polystyrene block copolymer blended with arandom copolymer of styrene and maleic anhydride, (c)polystyrene-polyisobutylene-polystyrene block copolymer blended with analternating copolymer of styrene and maleic anhydride having a molecularweight of approximately 50,000, (d)polystyrene-polyisobutylene-polystyrene block copolymer blended with analternating copolymer of styrene and maleic anhydride having a molecularweight of approximately 1700.

FIG. 5 illustrates cumulative release of paclitaxel as a function oftime for carrier layers containing paclitaxel and (a) apolystyrene-polyisobutylene-polystyrene block copolymer, (b) a randomcopolymer of styrene and maleic anhydride containing approximately 7 wt% maleic anhydride blended with apolystyrene-polyisobutylene-polystyrene block copolymer, and (c) arandom copolymer of styrene and maleic anhydride containingapproximately 14 wt % maleic anhydride blended with apolystyrene-polyisobutylene-polystyrene block copolymer, in accordancewith an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to the use of styrene copolymers inrelease layers that control the release of therapeutic agent from animplantable or insertable medical device.

By “release layer” is meant a layer that regulates the rate of releaseof a therapeutic agent. Two preferred release layers for use inaccordance with the present invention are carrier layers and barrierlayers.

By “carrier layer” is meant a layer which contains a therapeutic agentand from which the therapeutic agent is released.

By “barrier layer” is meant a layer which is disposed between a sourceof therapeutic agent and a site of intended release and which impedesthe rate at which the therapeutic agent is released.

According to one aspect of the present invention, a medical device isprovided which comprises an outer carrier layer disposed over at least aportion of an implantable or insertable medical device. The outercarrier layer comprises a styrene copolymer, an additional polymer and atherapeutic agent. Upon implantation or insertion of the device, thetherapeutic agent is released from the carrier layer in a controlledfashion.

According to another aspect of the present invention, an implantable orinsertable medical device is provided, which comprises (a) atherapeutic-agent-containing region and (b) a barrier layer comprising astyrene copolymer and an additional polymer over thetherapeutic-agent-containing region. Because the barrier layer isdisposed over the therapeutic-agent-containing region, the barrier layeracts to control release of the therapeutic agent from the medical deviceafter implantation or insertion of the same.

Preferred implantable or insertable medical devices for use inconjunction with the present invention include catheters (for example,renal or vascular catheters such as balloon catheters), guide wires,balloons, filters (e.g., vena cava filters), stents (including coronaryvascular stents, cerebral, urethral, ureteral, biliary, tracheal,gastrointestinal and esophageal stents), stent grafts, cerebral aneurysmfiller coils (including GDC—Guglilmi detachable coils—and metal coils),vascular grafts, myocardial plugs, patches, pacemakers and pacemakerleads, heart valves, biopsy devices, or any coated substrate (which cancomprise, for example, glass, metal, polymer, ceramic and combinationsthereof) that is implanted or inserted into the body, either forprocedural use or as an implant, and from which therapeutic agent isreleased.

The medical devices contemplated for use in connection with the presentinvention include drug delivery medical devices that are used for eithersystemic treatment or for the localized treatment of any mammaliantissue or organ. Non-limiting examples are tumors; organs including butnot limited to the heart, coronary and peripheral vascular system(referred to overall as “the vasculature”), lungs, trachea, esophagus,brain, liver, kidney, bladder, urethra and ureters, eye, intestines,stomach, pancreas, ovary, and prostate; skeletal muscle; smooth muscle;breast; cartilage; and bone.

One particularly preferred medical device for use in connection with thepresent invention is a vascular stent, which delivers therapeutic agentinto the vasculature for the treatment of restenosis. As used herein,“treatment” refers to the prevention of a disease or condition, thereduction or elimination of symptoms associated with a disease orcondition, or the substantial or complete elimination a disease orcondition. Preferred subjects are mammalian subjects and more preferablyhuman subjects.

“Therapeutic agents”, “pharmaceutically active agents”,“pharmaceutically active materials”, “drugs” and other related terms maybe used interchangeably herein and include genetic therapeutic agents,non-genetic therapeutic agents and cells. Therapeutic agents may be usedsingly or in combination.

Exemplary non-genetic therapeutic agents for use in connection with thepresent invention include: (a) anti-thrombotic agents such as heparin,heparin derivatives, urokinase, and PPack (dextrophenylalanine prolinearginine chloromethylketone); (b) anti-inflammatory agents such asdexamethasone, prednisolone, corticosterone, budesonide, estrogen,sulfasalazine and mesalamine; (c)antineoplastic/antiproliferative/anti-miotic agents such as paclitaxel,5-fluorouracil, cisplatin, vinblastine, vincristine, epothilones,endostatin, angiostatin, angiopeptin, monoclonal antibodies capable ofblocking smooth muscle cell proliferation, and thymidine kinaseinhibitors; (d) anesthetic agents such as lidocaine, bupivacaine andropivacaine; (e) anti-coagulants such as D-Phe-Pro-Arg chloromethylketone, an RGD peptide-containing compound, heparin, hirudin,antithrombin compounds, platelet receptor antagonists, anti-thrombinantibodies, anti-platelet receptor antibodies, aspirin, prostaglandininhibitors, platelet inhibitors and tick antiplatelet peptides; (f)vascular cell growth promoters such as growth factors, transcriptionalactivators, and translational promotors; (g) vascular cell growthinhibitors such as growth factor inhibitors, growth factor receptorantagonists, transcriptional repressors, translational repressors,replication inhibitors, inhibitory antibodies, antibodies directedagainst growth factors, bifunctional molecules consisting of a growthfactor and a cytotoxin, bifunctional molecules consisting of an antibodyand a cytotoxin; (h) protein kinase and tyrosine kinase inhibitors(e.g., tyrphostins, genistein, quinoxalines); (i) prostacyclin analogs;(j) cholesterol-lowering agents; (k) angiopoietins; (l) antimicrobialagents such as triclosan, cephalosporins, aminoglycosides andnitrofurantoin; (m) cytotoxic agents, cytostatic agents and cellproliferation affectors; (n) vasodilating agents; and (o) agents thatinterfere with endogenous vascoactive mechanisms.

Exemplary genetic therapeutic agents for use in connection with thepresent invention include anti-sense DNA and RNA as well as DNA codingfor: (a) anti-sense RNA, (b) tRNA or rRNA to replace defective ordeficient endogenous molecules, (c) angiogenic factors including growthfactors such as acidic and basic fibroblast growth factors, vascularendothelial growth factor, epidermal growth factor, transforming growthfactor α and β, platelet-derived endothelial growth factor,platelet-derived growth factor, tumor necrosis factor α, hepatocytegrowth factor and insulin-like growth factor, (d) cell cycle inhibitorsincluding CD inhibitors, and (e) thymidine kinase (“TK”) and otheragents useful for interfering with cell proliferation. Also of interestis DNA encoding for the family of bone morphogenic proteins (“BMP's”),including BMP-2, BMP-3, BMP-4, BMP-5, BMP-6 (Vgr-1), BMP-7 (OP-1),BMP-8, BMP-9, BMP-10, BMP-11, BMP-12, BMP-13, BMP-14, BMP-15, andBMP-16. Currently preferred BMP's are any of BMP-2, BMP-3, BMP-4, BMP-5,BMP-6 and BMP-7. These dimeric proteins can be provided as homodimers,heterodimers, or combinations thereof, alone or together with othermolecules. Alternatively, or in addition, molecules capable of inducingan upstream or downstream effect of a BMP can be provided. Suchmolecules include any of the “hedgehog” proteins, or the DNA's encodingthem.

Vectors for delivery of genetic therapeutic agents include (a) plasmids,(b) viral vectors such as adenovirus, adenoassociated virus andlentivirus, and (c) non-viral vectors such as lipids, liposomes andcationic lipids.

Cells for use in connection with the present invention include cells ofhuman origin (autologous or allogeneic), including stem cells, or froman animal source (xenogeneic), which can be genetically engineered, ifdesired, to deliver proteins of interest.

Numerous therapeutic agents, not necessarily exclusive of those listedabove, have been identified as candidates for vascular treatmentregimens, for example, as agents targeting restenosis. Such agents areuseful for the practice of the present invention and include one or moreof the following: (a) Ca-channel blockers including benzothiazapinessuch as diltiazem and clentiazem, dihydropyridines such as nifedipine,amlodipine and nicardapine, and phenylalkylamines such as verapamil, (b)serotonin pathway modulators including: 5-HT antagonists such asketanserin and naftidrofuryl, as well as 5-HT uptake inhibitors such asfluoxetine, (c) cyclic nucleotide pathway agents includingphosphodiesterase inhibitors such as cilostazole and dipyridamole,adenylate/Guanylate cyclase stimulants such as forskolin, as well asadenosine analogs, (d) catecholamine modulators including α-antagonistssuch as prazosin and bunazosine, β-antagonists such as propranolol andα/β-antagonists such as labetalol and carvedilol, (e) endothelinreceptor antagonists, (f) nitric oxide donors/releasing moleculesincluding organic nitrates/nitrites such as nitroglycerin, isosorbidedinitrate and amyl nitrite, inorganic nitroso compounds such as sodiumnitroprusside, sydnonimines such as molsidomine and linsidomine,nonoates such as diazenium diolates and NO adducts of alkanediamines,S-nitroso compounds including low molecular weight compounds (e.g.,S-nitroso derivatives of captopril, glutathione and N-acetylpenicillamine) and high molecular weight compounds (e.g., S-nitrosoderivatives of proteins, peptides, oligosaccharides, polysaccharides,synthetic polymers/oligomers and natural polymers/oligomers), as well asC-nitroso-compounds, O-nitroso-compounds, N-nitroso-compounds andL-arginine, (g) ACE inhibitors such as cilazapril, fosinopril andenalapril, (h) ATII-receptor antagonists such as saralasin and losartin,(i) platelet adhesion inhibitors such as albumin and polyethylene oxide,(j) platelet aggregation inhibitors including aspirin and thienopyridine(ticlopidine, clopidogrel) and GP IIb/IIIa inhibitors such as abciximab,epitifibatide and tirofiban, (k) coagulation pathway modulatorsincluding heparinoids such as heparin, low molecular weight heparin,dextran sulfate and β-cyclodextrin tetradecasulfate, thrombin inhibitorssuch as hirudin, hirulog, PPACK(D-phe-L-propyl-L-arg-chloromethylketone)and argatroban, FXa inhibitors such as antistatin and TAP (tickanticoagulant peptide), Vitamin K inhibitors such as warfarin, as wellas activated protein C, (l) cyclooxygenase pathway inhibitors such asaspirin, ibuprofen, flurbiprofen, indomethacin and sulfinpyrazone, (m)natural and synthetic corticosteroids such as dexamethasone,prednisolone, methprednisolone and hydrocortisone, (n) lipoxygenasepathway inhibitors such as nordihydroguairetic acid and caffeic acid,(o) leukotriene receptor antagonists, (p) antagonists of E- andP-selectins, (q) inhibitors of VCAM-1 and ICAM-1 interactions, (r)prostaglandins and analogs thereof including prostaglandins such as PGE1and PGI2 and prostacyclin analogs such as ciprostene, epoprostenol,carbacyclin, iloprost and beraprost, (s) macrophage activationpreventers including bisphosphonates, (t) HMG-CoA reductase inhibitorssuch as lovastatin, pravastatin, fluvastatin, simvastatin andcerivastatin, (u) fish oils and omega-3-fatty acids, (v) free-radicalscavengers/antioxidants such as probucol, vitamins C and E, ebselen,trans-retinoic acid and SOD mimics, (w) agents affecting various growthfactors including FGF pathway agents such as bFGF antibodies andchimeric fusion proteins, PDGF receptor antagonists such as trapidil,IGF pathway agents including somatostatin analogs such as angiopeptinand ocreotide, TGF-β pathway agents such as polyanionic agents (heparin,fucoidin), decorin, and TGF-β antibodies, EGF pathway agents such as EGFantibodies, receptor antagonists and chimeric fusion proteins, TNF-αpathway agents such as thalidomide and analogs thereof, Thromboxane A2(TXA2) pathway modulators such as sulotroban, vapiprost, dazoxiben andridogrel, as well as protein tyrosine kinase inhibitors such astyrphostin, genistein and quinoxaline derivatives, (x) MMP pathwayinhibitors such as marimastat, ilomastat and metastat, (y) cell motilityinhibitors such as cytochalasin B, (z) antiproliferative/antineoplasticagents including antimetabolites such as purineanalogs(6-mercaptopurine), pyrimidine analogs (e.g., cytarabine and5-fluorouracil) and methotrexate, nitrogen mustards, alkyl sulfonates,ethylenimines, antibiotics (e.g., daunorubicin, doxorubicin),nitrosoureas, cisplatin, agents affecting microtubule dynamics (e.g.,vinblastine, vincristine, colchicine, paclitaxel and epothilone),caspase activators, proteasome inhibitors, angiogenesis inhibitors(e.g., endostatin, angiostatin and squalamine), rapamycin, cerivastatin,flavopiridol and suramin, (aa) matrix deposition/organization pathwayinhibitors such as halofuginone or other quinazolinone derivatives andtranilast, (bb) endothelialization facilitators such as VEGF and RGDpeptide, and (cc) blood rheology modulators such as pentoxifylline.

Numerous additional therapeutic agents useful for the practice of thepresent invention are also disclosed in U.S. Pat. No. 5,733,925 assignedto NeoRx Corporation, the entire disclosure of which is incorporated byreference.

A wide range of therapeutic agent loadings can be used in connectionwith the medical devices of the present invention, with the amount ofloading being readily determined by those of ordinary skill in the artand ultimately depending, for example, upon the condition to be treated,the nature of the therapeutic agent itself, the means by which thetherapeutic agent is administered to the intended subject, and so forth.

The present invention utilizes release layers comprising a styrenecopolymer and an additional polymer.

A “styrene copolymer” is a polymer formed from two or more dissimilarmonomers, at least one of which is styrene, or a styrene derivative(e.g., alpha-methyl styrene, ring-alkylated styrenes or ring-halogenatedstyrenes, or other substituted styrenes where one or more substituentsare present on the aromatic ring). Such copolymers may be, for example,random copolymers, alternating copolymers, block copolymers or graftcopolymers, and may be, for example, linear, star-shaped, or branched inform. Copolymers comprising random polymer chains formed from two ormore dissimilar monomers, at least one of which is styrene or a styrenederivative (referred to herein as “random styrene copolymers”) andcopolymers comprising alternating polymer chains formed from two or moredissimilar monomers, at least one of which is styrene or a styrenederivative (referred to herein as “alternating styrene copolymers”) arepreferred.

Examples of styrene copolymers for the practice of the present inventioninclude copolymers of: (1) a monomer of styrene or a styrene derivativewith (2) at least one additional monomer, preferably selected fromunsaturated monomers such as: (a) alkylene monomers, such as ethylene,propylene, butadiene, butylenes (e.g., butylene, isobutylene), andisoprene; (b) halogenated alkylene monomers (e.g., tetrafluoroethyleneand chloroethylene); (c) vinyl monomers and derivatives, such as, methylvinyl ether, vinyl acetate, vinyl ethylene (butadiene), vinyl chloride,vinyl pyrrolidone, vinyl cyanide (acrylonitrile), and vinyl alcohol; (d)acrylic acid monomers and derivatives, such as methyl acrylate, methylmethacrylate, acrylic acid, methacrylic acid, hydroxyethyl acrylate,hydroxyethyl methacrylate, glyceryl acrylate, glyceryl methacrylate,acrylamide, methacrylamide and ethacrylamide; and (e) maleic anhydridemonomers and derivatives, including maleic anhydride, maleic anhydridein a free acid form, maleic anhydride in a salt form, and maleicanhydride in a partial ester form.

Specific examples of styrene copolymers includeacrylonitrile-butadiene-styrene copolymers, acrylonitrile-chlorinatedpolyethylene-styrene copolymers, acrylonitrile-styrene-acrylatecopolymers, acrylonitrile-ethylene-propylene-styrene copolymers,ethylene-styrene copolymers, methyl methacrylate-butadiene-styrenecopolymers, methyl methacrylate-acrylonitrile-butadiene-styrenecopolymers, olefin modified styrene acrylonitrile copolymers,butadiene-styrene copolymers, styrene-isoprene copolymers,styrene-acrylonitrile copolymers, styrene-ethylene-butylene copolymers,styrene-maleic anhydride copolymers, and styrene-methyl methacrylatecopolymers.

In forming the release layers of the present invention, the styrenecopolymers are blended or crosslinked with one or more additionalpolymers. The additional polymers may be, for example, homopolymers orcopolymers, crosslinked or uncrosslinked, linear or branched, natural orsynthetic, thermoplastic or thermosetting.

Additional polymers include the following: polycarboxylic acid polymersand copolymers including polyacrylic acids (e.g., acrylic latexdispersions and various polyacrylic acid products such as HYDROPLUS,available from Boston Scientific Corporation, Natick, Mass. anddescribed in U.S. Pat. No. 5,091,205, the disclosure of which is herebyincorporated herein by reference, and HYDROPASS, also available fromBoston Scientific Corporation); acetal polymers and copolymers; acrylateand methacrylate polymers and copolymers; cellulosic polymers andcopolymers, including cellulose acetates, cellulose nitrates, cellulosepropionates, cellulose acetate butyrates, cellophanes, rayons, rayontriacetates, and cellulose ethers such as carboxymethyl celluloses andhydoxyalkyl celluloses; polyoxymethylene polymers and copolymers;polyimide polymers and copolymers such as polyether block imides,polyamidimides, polyesterimides, and polyetherimides; polysulfonepolymers and copolymers including polyarylsulfones andpolyethersulfones; polyamide polymers and copolymers including nylon6,6, polycaprolactams and polyacrylamides; resins including alkydresins, phenolic resins, urea resins, melamine resins, epoxy resins,allyl resins and epoxide resins; polycarbonates; polyacrylonitriles;polyvinylpyrrolidones (cross-linked and otherwise); polymers andcopolymers of vinyl monomers including polyvinyl alcohols, polyvinylhalides such as polyvinyl chlorides, ethylene-vinylacetate copolymers(EVA), polyvinylidene chlorides, polyvinyl ethers such as polyvinylmethyl ethers, polystyrenes, styrene-butadiene copolymers,acrylonitrile-styrene copolymers, acrylonitrile-butadiene-styrenecopolymers, styrene-butadiene-styrene copolymers andstyrene-isobutylene-styrene copolymers, polyvinyl ketones,polyvinylcarbazoles, and polyvinyl esters such as polyvinyl acetates;polybenzimidazoles; ionomers; polyalkyl oxide polymers and copolymersincluding polyethylene oxides (PEO); glycosaminoglycans; polyestersincluding polyethylene terephthalates and aliphatic polyesters such aspolymers and copolymers of lactide (which includes lactic acid as wellas d-, l- and meso lactide), epsilon-caprolactone, glycolide (includingglycolic acid), hydroxybutyrate, hydroxyvalerate, para-dioxanone,trimethylene carbonate (and its alkyl derivatives), 1,4-dioxepan-2-one,1,5-dioxepan-2-one, and 6,6-dimethyl-1,4-dioxan-2-one (a copolymer ofpolylactic acid and polycaprolactone is one specific example); polyetherpolymers and copolymers including polyarylethers such as polyphenyleneethers, polyether ketones, polyether ether ketones; polyphenylenesulfides; polyisocyanates (e.g., U.S. Pat. No. 5,091,205 describesmedical devices coated with one or more polyisocyanates such that thedevices become instantly lubricious when exposed to body fluids);polyolefin polymers and copolymers, including polyalkylenes such aspolypropylenes, polyethylenes (low and high density, low and highmolecular weight), polybutylenes (such as polybut-1-ene andpolyisobutylene), poly-4-methyl-pen-1-enes, ethylene-alpha-olefincopolymers, ethylene-methyl methacrylate copolymers and ethylene-vinylacetate copolymers; fluorinated polymers and copolymers, includingpolytetrafluoroethylenes (PTFE),poly(tetrafluoroethylene-co-hexafluoropropene) (FEP), modifiedethylene-tetrafluoroethylene copolymers (ETFE), and polyvinylidenefluorides (PVDF); silicone polymers and copolymers; polyurethanes (e.g.,BAYHYDROL polyurethane dispersions); p-xylylene polymers;polyiminocarbonates; copoly(ether-esters) such as polyethyleneoxide-polylactic acid copolymers; polyphosphazines; polyalkyleneoxalates; polyoxaamides and polyoxaesters (including those containingamines and/or amido groups); polyorthoesters; biopolymers, such aspolypeptides, proteins, polysaccharides and fatty acids (and estersthereof), including fibrin, fibrinogen, collagen, elastin, chitosan,gelatin, starch, glycosaminoglycans such as hyaluronic acid; as well asblends and copolymers of the above.

Some exemplary additional polymers for use in combination with thepresent invention are block copolymers comprising at least two polymericblocks A and B. Examples of such block copolymers include the following:(a) BA (linear diblock), (b) BAB or ABA (linear triblock), (c) B(AB)_(n)or A(BA)_(n) (linear alternating block), or (d) X-(AB)_(n) or X-(BA)_(n)(includes diblock, triblock and other radial block copolymers), where nis a positive whole number and X is a starting seed, or initiator,molecule.

One specifically preferred group of polymers have X-(AB)_(n) structures,which are frequently referred to as diblock copolymers and triblockcopolymers where n=1 and n=2, respectively (this terminology disregardsthe presence of the starting seed molecule, for example, treating A-X-Aas a single A block with the triblock therefore denoted as BAB). Wheren=3 or more, these structures are commonly referred to as star-shapedblock copolymers.

Other examples of additional polymers include branched block copolymerssuch as dendritic block copolymers (e.g., arborescent block copolymers),wherein at least one of the A and B blocks is branched, and preferablywherein the A blocks are branched and capped by the B blocks.

The A blocks are preferably soft elastomeric components which are basedupon one or more polyolefins or other polymer with a glass transitiontemperature at or below room temperature. For example, the A blocks canbe polyolefinic blocks having alternating quaternary and secondarycarbons of the general formulation: —(CRR′—CH₂)_(n)—, where R and R′ arelinear or branched aliphatic groups such as methyl, ethyl, propyl,isopropyl, butyl, isobutyl and so forth, or cyclic aliphatic groups suchas cyclohexane, cyclopentane, and the like, with and without pendantgroups. Preferred polyolefinic blocks include blocks of isobutylene,

(i.e., polymers where R and R′ are the same and are methyl groups).Other examples of A blocks include silicone rubber blocks and acrylaterubber blocks.

The B blocks are preferably hard thermoplastic blocks with glasstransition temperatures significantly higher than the elastomeric Ablock that, when combined with the soft A blocks, are capable of, interalia, altering or adjusting the hardness of the resulting copolymer toachieve a desired combination of qualities. Preferred B blocks arepolymers of methacrylates or polymers of vinyl aromatics. More preferredB blocks are (a) made from monomers of styrene

styrene derivatives (e.g., α-methylstyrene, ring-alkylated styrenes orring-halogenated styrenes or other substituted styrenes where one ormore substituents are present on the aromatic ring) or mixtures of thesame, collectively referred to herein as “styrenic blocks” or“polystyrenic blocks” or are (b) made from monomers ofmethylmethacrylate, ethylmethacrylate hydroxyethyl methacrylate ormixtures of the same.

More preferred are additional polymers that are elastomeric. As definedherein, an “elastomeric” polymer is a polymer that can be stretched toat least 1.5 times its original length at room temperature and, uponrelease of the stretching stress, will return with force to itsapproximate original length.

In some particularly preferred embodiments of the present invention, astyrene copolymer is combined with one or more of the followingelastomers: (a) a copolymer of polyisobutylene with polystyrene orpoly-alpha-methylstyrene, more preferablypolystyrene-polyisobutylene-polystyrene triblock copolymers which, alongwith other polymers appropriate for the practice of the presentinvention, are described, for example, in U.S. Pat. No. 5,741,331, U.S.Pat. No. 4,946,899 and U.S. Ser. No. 09/734,639, each of which is herebyincorporated by reference in its entirety; (b) a copolymer containingone or more blocks of polystyrene and one or more random polymer blocksof ethylene and butylene, for example, apolystyrene-polyethylene/butylene-polystyrene (SEBS) block copolymer,available as Kraton™ G series polymers available from Kraton Polymers;(c) a homopolymer of n-butyl methacrylate (BMA); and (d) arborescentpolyisobutylene-polystyrene block copolymers such as those described inKwon et al., “Arborescent Polyisobutylene-Polystyrene Block Copolymers-aNew Class of Thermoplastic Elastomers,” Polymer Preprints, 2002, 43(1),266, which is hereby incorporated by reference in its entirety.

The release characteristics associated with the release layers of thepresent invention can be varied in a number of ways, including thefollowing: (a) varying the type of styrene copolymer(s) used within therelease layer, (b) varying the molecular weight of the styrenecopolymer(s) used within the release layer, (c) varying the relativeamount of styrene monomer in the copolymer, relative to the othermonomers, and (d) varying the type, molecular weight and/or relativeamount of the additional polymer. Several of these effects aredemonstrated in the Examples below.

Medical devices having a sustained release profile are preferred in manycases. By “sustained release profile” is meant a release profile inwhich less than 25% of the total release from the medical device thatoccurs over the course of implantation/insertion in the body occurswithin the first 1-3 days of administration. Conversely, this means thatmore than 75% of the total release from the medical device will occurafter the device has been implanted/inserted for 1-3 days.

In general, the release layers of the present invention are formed usingany number of known techniques. Solvent-based techniques, in which thestyrene copolymer and the additional polymer are dissolved or dispersedin a solvent prior to layer formation, are preferred.

Where solvent-based techniques are used, the solvent system that isselected will contain one or more solvent species. The solvent systempreferably is a good solvent for the polymers and, where included, forthe therapeutic agent as well. The particular solvent species that makeup the solvent system may also be selected based on othercharacteristics including drying rate and surface tension.

Solvent species that can be used in connection with the presentinvention include any combination of one or more of the following: (a)water, (b) alkanes such as ethane, hexane, octane, cyclohexane, heptane,isohexane, butane, pentane, isopentane, 2,2,4-trimethlypentane, nonane,decane, dodecane, hexadecane, eicosane, methylcyclohexane,cis-decahydronaphthalene and trans-decahydronaphthalene, (c) aromaticspecies such as benzene, toluene, xylene(s), naphthalene, styrene,ethylbenzene, 1-methylnaphthalene, 1,3,5-trimethylbenzene,tetrahydronaphthalene, diphenyl and 1,4-diethylbenzene, (d)halohydrocarbons including (i) chlorohyhdrocarbons such as chloroform,methyl chloride, dichloromethane, 1,1-dichloroethylene, ethylenedichloride, ethylidene chloride, propyl chloride, cyclohexyl chloride,1,1,1-trichloroethane, perchloroethylene, trichloroethylene, butylchloride, carbon tetrachloride, tetrachloroethylene, chlorobenzene,o-dichlorobenzene, benzyl chloride, trichlorobiphenyl,methylcyclohexane, 1,1,2,2-tetrachloroethane (ii) fluorinatedhalogenated species such as chlorodiflouoromethane,dichlorofluoromethane, dichlorodifluoromethane, trichlorofluoromethane,1,2-dichlorotetrafluoroethane, 1,1,2-trichlorotrifluoroethane,perfluor(methylcyclohexane), perfluor(dimethylcyclohexane) and (iii)other halohydrocarbons such as ethyl bromide, ethylidene bromide,ethylene dibromide, tribromomethane, bromotrifluoromethane,1,1,2,2-tetrabromoethane, bromobenzene, bromochloromethane,1-bromonaphthalene, methyl iodide, methylene diiodide (e) acidaldehydes/anhydrides such as acetaldehyde, furfural, butyraldehyde,benzaldehyde, acetyl chloride, succinic anhydride and acetic anhydride,(f) alcohols including (i) phenols such as phenol, 1,3-benzenediol,m-cresol, o-methoxyphenol, methyl salicylate and nonylphenol, (ii)polyhydric alcohols such as ethylene glycol, glycerol, propylene glycol,1,3-butanediol, diethylene glycol, triethylene glycol, hexylene glycoland dipropylene glycol, and (iii) other alcohols such as methanol,ethanol, ethylene cyanohydrin, allyl alcohol, 1-propanol, 2-propanol,3-chloropropanol, furfuryl alcohol, 1-butanol, 2-butanol, benzylalcohol, isobutanol, cyclohexanol, I-pentanol, 2-ethyl-1-butanol,diacetone alcohol, 1,3-dimethyl-1-butanol, ethyl lactate, butyl lactate,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,ethylene glycol monobutyl ether, 2-ethyl-1-hexanol, 1-octanol,2-octanol, diethylene glycol monobutyl ether, 1-decanol, 1-tridecylalcohol, nonyl-phenoxy ethanol, oleyl alcohol, triethylene glycolmono-oleyl ether, (g) ethers such as, epichlorohydrin, furan,1,4-dioxane, dimethoxymethane, diethyl ether, bis-(2-chloroethyl) ether,anisole, di-(2-methoxyethyl) ether, dibenzyl ether,di-(2-chloroisopropyl) ether, bis-(m-phenoxyphenol) ether, dimethylether and tetrahydrofuran, (h) ketones, such as acetone, cylohexanone,isophorone, diethyl ketone, mesityl oxide, acetophenone, methyl ethylketone, methyl isoamyl ketone, methyl isobutyl ketone, and methyl propylketone, (i) acids such as formic acid, acetic acid, benzoic acid,butyric acid, octanoic acid, oleic acid, stearic acid, (j)esters/acetates such as ethylene carbonate, butyrolactone,propylene-1,2-carbonate, ethyl chloroformate, ethyl acetate, trimethylphosphate, diethyl carbonate, diethyl sulfate, ethyl formate, methylacetate, n-butyl acetate, isobutyl acetate, t-butyl acetate,2-ethoxyethyl acetate, isoamyl acetate, dimethyl phthalate, ethylcinnamate, triethyl phosphate, diethyl phosphate, butyl benzylphthalate, dibutyl phthalate, diethyl phthalate, tricrysyl phosphate,tributyl phosphate, dibutyl sebacate, methyl oleate, dioctyl phthalate,dibutyl stearate isopropyl acetate, isobutyl isobutyrate, n-propylacetate and n-butyl propionate, (k) nitrogen compounds such asacetonitrile, acrylonitrile, propionitrile, butyronitrile, nitromethane,nitroethane, 2-nitropropane, nitrobenzene, ethanolamine,ethylenediamine, 1,1-dimethylhydrazine, 2-pyrrolidone, pyridine,propylamine, morpholine, analine, n-methyl-2-pyrrolidone, butylamine,diethylamine, cyclohexylamine, quinoline, dipropylamine, formamide,n,n-dimethylformamide, n,n-dimethylacetamide, tetramethylurea,hexamethyl phosphoramide, diethylenetriamine, triethylamine andtriethanolamine, and (l) sulfur compounds such as carbon disulfide,dimethylsulfoxide, ethanethiol, dimethyl sulfone and diethyl sulfide.

Preferred solvent-based techniques include, but are not limited to,solvent casting techniques, spin coating techniques, web coatingtechniques, solvent spraying techniques, dipping techniques, techniquesinvolving coating via mechanical suspension, including air suspension,ink jet techniques, electrostatic techniques, and combinations of theseprocesses. Typically, a solution containing solvent and polymers (and,in some cases, a therapeutic agent) is applied to a substrate to form arelease layer (e.g., a carrier layer or barrier layer). The substrate istypically all or a portion of an implantable or insertable medicaldevice, to which the release layer is applied.

Where appropriate, techniques such as those listed above can be repeatedor combined to build up a release layer to a desired thickness. Thethickness of the release layer can be varied in other ways as well. Forexample, in one preferred process, solvent spraying, coating thicknesscan be increased by modification of coating process parameters,including increasing spray flow rate, slowing the movement between thesubstrate to be coated and the spray nozzle, providing repeated passesand so forth.

In the case of a carrier layer, for example, a therapeutic agent can beincluded in the above-described polymer solution if desired, and henceco-established with the carrier layer. In other embodiments, on theother hand, the therapeutic agent can be dissolved or dispersed within asolvent, and the resulting solution contacted with a previously formedlayer, for example, using one or more of the solvent based applicationtechniques described above (e.g., dipping, spraying, etc.).

Barrier layers, on the other hand, are formed over atherapeutic-agent-containing region. In some embodiments, however, thetherapeutic-agent-containing region comprises one or more polymers,which can be selected, for example, from the polymers listed above. Assuch, the therapeutic-agent-containing region can also be establishedusing solvent-based techniques (e.g., dipping, spraying, etc.) such asthose discussed above. In other embodiments, thetherapeutic-agent-containing region beneath the barrier layer isestablished without an associated polymer. For example, the therapeuticagent can simply be dissolved or dispersed in a liquid, and theresulting solution/dispersion contacted with a substrate, for instance,using one or more of the above-described application techniques.

Where the release layer is formed using a solvent based technique, it ispreferably dried after application to remove the solvents. The releaselayer typically further conforms to the underlying surface during thedrying process.

The invention is further described with reference to the followingnon-limiting Examples.

Example 1

A solution is provided that contains 25 weight % tetrahydrofuran (THF),74 wt % toluene, 0.25 wt % paclitaxel and 0.75 wt % of a polymercomposition or blend.

One control solution is prepared by mixing 0.75 wt % of the blockcopolymer polystyrene-polyisobutylene-polystyrene block copolymer (SIBS)with the solvents and paclitaxel. The SIBS copolymer is synthesizedusing known techniques such as those described in U.S. Pat. No.5,741,331, U.S. Pat. No. 4,946,899 and U.S. Ser. No. 09/734,639.

A first corresponding test solution contains 0.65 wt % of the SIBScopolymer and 0.10 wt % of a random copolymer of styrene and maleicanhydride containing approximately 14 wt % maleic anhydride (SMA14). TheSMA14 copolymer is purchased from Sigma-Aldrich, or is available fromNova Chemical as Dylark 332.

Another control solution is prepared by mixing 0.75 wt % of thehomopolymer poly(butyl methacrylate) (BMA) with the solvents andpaclitaxel. BMA may be purchased from Sigma-Aldrich at a molecularweight of 337,000.

A second test solution containing 0.65 wt % of the BMA homopolymer and0.10 wt % of SMA14 copolymer in prepared.

A third control solution is prepared with 0.75 wt % of apolystyrene-b-poly(ethylene-r-butylene)-b-polystyrene block copolymer(SEBS). The SEBS copolymer is obtained from Sigma-Aldrich, but is alsoknown by the trade name Kraton™.

A third test solution is prepared using 0.65 wt % of the SEBS copolymerand 0.10 wt % of the SMA 14 copolymer.

All solutions are prepared by (1) mixing the paclitaxel andtetrahydrofuran, (2) adding the copolymer or copolymers, (3) adding thetoluene, (4) thoroughly mixing (e.g., overnight), and (5) filtering.

The solution is then placed in a syringe pump and fed to a spray nozzle.A stent is mounted onto a holding device parallel to the nozzle and, ifdesired, rotated to ensure uniform coverage. Depending on the sprayequipment used, either the component or spray nozzle can be moved whilespraying such that the nozzle moves along the component while sprayingfor one or more passes. After a carrier coating is formed in thisfashion, the stent is dried, for example, by placing it in a preheatedoven for 30 minutes at 65° C., followed by 3 hours at 70° C.

Three stents are formed in this manner for each of the various polymericsolutions. Paclitaxel release is then measured as a function of time inPBS with 0.5 wt % Tween® 20 (polyoxyethylene (20) sorbitan monolaurate)available from Sigma-Aldrich. The results, presented as the cumulativerelease of paclitaxel as a function of time, are graphically illustratedin FIG. 1.

These results indicate that the release rate of a therapeutic agent fromvarious polymeric carrier layers can be modulated by the addition ofrandom copolymer containing styrene and maleic anhydride.

Example 2

A series of solutions are prepared in a procedure similar to theprocedure used in Example 1. All solutions contain the following: 25 wt% tetrahydrofuran (THF), 74 wt % toluene, 0.25 wt % paclitaxel and 0.75wt % of a polymer composition or blend.

The control solutions are prepared by mixing 0.75 wt % the SIBScopolymer (see Example 1) or 0.75 wt % of the SMA14 copolymer (seeExample 1) with the solvents and paclitaxel.

Test solutions are made containing the following polymeric constituents:(a) 0.5 wt % SMA14 and 0.25 wt % SIBS, (b) 0.3 wt % SMA14 and 0.45 wt %SIBS, (c) 0.2 wt % SMA14 and 0.55 wt % SIBS, (d) 0.1 wt % SMA14 and 0.55wt % SIBS, (e) 0.15 wt % SMA14 and 0.60 wt % SIBS, (f) 0.1 wt % SMA14and 0.65 wt % SIBS (two data sets), and (g) 0.05 wt % SMA14 and 0.7 wt %SIBS.

The solutions are applied to stents and dried according to theprocedures of Example 1. Three stents are coated using each of the abovesolutions. The cumulative release of paclitaxel as a function of time isthen measured as in Example 1. The results are graphically illustratedin FIGS. 2A and 2B.

These results indicate that the release rate of a therapeutic agent froma carrier layer comprising a polymeric carrier can be modulated by theaddition of a random copolymer containing styrene and maleic anhydridein various proportions.

Example 3

A series of solutions are prepared in a procedure similar to theprocedure used in Example 1. All solutions contain the following: 25 wt% tetrahydrofuran (THF), 74 wt % toluene, 0.25 wt % paclitaxel and 0.75wt % of a polymer or blend.

The control solution (two data sets) is prepared by mixing 0.75 wt % ofthe SIBS copolymer (see Example 1) with the solvents and paclitaxel.

Test solutions are made containing the following polymeric constituents:(a) 0.3 wt % styrene-co-acrylonitrile random copolymer containingapproximately 25 wt % acrylonitrile (SAN25) and 0.45 wt % SIBS, (b) 0.10wt % SAN25 and 0.65 wt % SIBS. SAN25 may be purchased from Sigma-Aldrichat a molecular weight of 165,000.

The solutions are applied to stents and dried according to theprocedures of Example 1. Three stents are coated using each of the abovesolutions. The cumulative release of paclitaxel as a function of time isthen measured as in Example 1. The results are graphically illustratedin FIG. 3.

These results indicate that the release rate of a therapeutic agent froma carrier layer comprising a polymeric carrier can be modulated by theaddition of a copolymer of styrene and acrylonitrile in variousproportions.

Example 4

A series of solutions are prepared in a procedure like that used inExample 1. All solutions contain the following: 25 wt % tetrahydrofuran(THF), 74 wt % toluene, 0.25 wt % paclitaxel and 0.75 wt % polymer.

A control solution is prepared using 0.75 wt % of the SIBS copolymer(see Example 1).

A first test solution is prepared using 0.1% SMA14, a random copolymerof styrene and maleic anhydride containing approx. 14 wt % maleicanhydride (see Example 1) and 0.65% SIBS.

A second test solution is prepared using 0.722 wt % SIBS copolymer and0.028 wt % of an alternating copolymer of styrene and maleic anhydride(SMA50) having a molecular weight of approximately 50,000, purchasedfrom Scientific Polymer Products, Inc.

A third test solution is prepared using 0.722 wt % SIBS copolymer and0.028 wt % of an alternating copolymer of styrene and maleic anhydride(SMA50) having a molecular weight of approximately 1700, also purchasedfrom Scientific Polymer Products, Inc.

Note that the maleic anhydride (MA) content is the same for all testsolutions.SMA14: 14% MA×10% SMA=1.4% MA totalSMA50: 50% MA×2.8% SMA=1.4% MA total

The solutions are applied to stents and dried according to theprocedures of Example 1. Three stents are coated from each of the abovesolutions. The cumulative release of paclitaxel as a function of time isthen measured as in Example 1. The results are graphically illustratedin FIG. 4.

These results indicate that the release rate of a therapeutic agent froma carrier layer comprising a copolymer of maleic anhydride and styrenecan be modulated by varying the molecular weight of the copolymer in thecarrier layer.

Example 5

A series of solutions are prepared in a procedure like that used inExample 1. All solutions contain the following: 25 wt % tetrahydrofuran(THF), 74 wt % toluene, 0.25 wt % paclitaxel and 0.75 wt % polymer.

A control solution is prepared using 0.75 wt % of the SIBS copolymer(see Example 1).

A first test solution is prepared using 0.1% SMA14, a random copolymerof styrene and maleic anhydride containing approx 14 wt % maleicanhydride (see Example 1) and 0.65% SIBS.

A second test solution is prepared using 0.1 wt % SMA7, a randomcopolymer of styrene and maleic anhydride containing approximately 7 wt% maleic anhydride, and 0.65% SIBS.

The solutions are applied to stents and dried according to theprocedures of Example 1. Three stents are coated from each of the abovesolutions. The cumulative release of paclitaxel as a function of time isthen measured as in Example 1. The results are graphically illustratedin FIG. 5.

These results indicate that the release rate of a therapeutic agent froma carrier layer containing a copolymer of maleic anhydride and styrenecan be increased by varying the relative amounts of maleic anhydridemonomer and styrene monomer in the copolymer.

Although various embodiments are specifically illustrated and describedherein, it will be appreciated that modifications and variations of thepresent invention are covered by the above teachings and are within thepurview of the appended claims without departing from the spirit andintended scope of the invention.

1. A therapeutic-agent-releasing medical device for the sustainedrelease of a therapeutic agent, said medical device comprising: (a) animplantable or insertable medical device; (b) a release layer disposedover at least a portion of the implantable or insertable medical device,said release layer comprising (i) a styrene copolymer, which is not ablock copolymer and which is not a graft copolymer, and (ii) anadditional polymer; and (c) a therapeutic agent, said release layerregulating the sustained release of the therapeutic agent from themedical device upon implantation or insertion of the device into apatient.
 2. The therapeutic-agent-releasing medical device of claim 1,wherein said release layer is a carrier layer that comprises saidtherapeutic agent.
 3. The therapeutic-agent-releasing medical device ofclaim 1, wherein said release layer is a barrier layer disposed over atherapeutic-agent-containing region that comprises said therapeuticagent.
 4. The therapeutic-agent-releasing medical device of claim 1,wherein said implantable or insertable medical device is selected from acatheter, a guide wire, a balloon, a filter, a stent, a stent graft, avascular graft, a vascular patch, a shunt, and an intraluminal pavingsystem.
 5. The therapeutic-agent-releasing medical device of claim 1,wherein said implantable or insertable medical device is adapted forimplantation or insertion into the coronary vasculature, peripheralvascular system, esophagus, trachea, colon, biliary tract, urinarytract, prostate or brain.
 6. The therapeutic-agent-releasing medicaldevice of claim 1, wherein said therapeutic agent is selected from oneor more of the group consisting of an anti-thrombotic agent, ananti-proliferative agent, an anti-inflammatory agent, an anti-migratoryagent, an agent affecting extracellular matrix production andorganization, an antineoplastic agent, an anti-mitotic agent, ananesthetic agent, an anti-coagulant, a vascular cell growth promoter, avascular cell growth inhibitor, a cholesterol-lowering agent, avasodilating agent, and an agent that interferes with endogenousvasoactive mechanisms.
 7. The therapeutic-agent-releasing medical deviceof claim 1, wherein said styrene copolymer is an alternating copolymer.8. The therapeutic-agent-releasing medical device of claim 1, whereinsaid styrene copolymer is a random copolymer.
 9. Thetherapeutic-agent-releasing medical device of claim 1, wherein saidstyrene copolymer is a random copolymer of styrene and maleic anhydride.10. The therapeutic-agent-releasing medical device of claim 1, whereinsaid styrene copolymer is a random copolymer of styrene andacrylonitrile.
 11. The therapeutic-agent-releasing medical device ofclaim 1, wherein said styrene copolymer is a copolymer comprising (a) amonomer comprising a carbon-carbon double bond and (b) a styrenemonomer.
 12. The therapeutic-agent-releasing medical device of claim 11,wherein said monomer comprising a carbon-carbon double bond is analkylene monomer.
 13. The therapeutic-agent-releasing medical device ofclaim 12, wherein said alkylene monomer is selected from ethylene,propylene, butadiene, butylene, isobutylene and isoprene.
 14. Thetherapeutic-agent-releasing medical device of claim 11, wherein saidmonomer comprising a carbon-carbon double bond is a vinyl monomer. 15.The therapeutic-agent-releasing medical device of claim 14, wherein saidvinyl monomer is selected from one or more of vinyl ethers, vinylacetates, vinyl aliphatics, halogenated vinyl compounds, vinylpyrrolidone, acrylonitrile, vinyl alcohols, and vinyl acrylamides. 16.The therapeutic-agent-releasing medical device of claim 11, wherein saidmonomer comprising a carbon-carbon double bond is an acrylic acidmonomer or acrylic acid derivative.
 17. The therapeutic-agent-releasingmedical device of claim 16, wherein said acrylic acid monomer orderivative is selected from methyl acrylate, methyl methacrylate,acrylic acid, methacrylic acid, hydroxyethyl acrylate, hydroxyethylmethacrylate, glyceryl acrylate, glyceryl methacrylate, acrylamide,methacrylamide and ethacrylamide.
 18. The therapeutic-agent-releasingmedical device of claim 11, wherein said monomer comprising acarbon-carbon double bond is maleic anhydride or a maleic anhydridederivative.
 19. The therapeutic-agent-releasing medical device of claim1, wherein said additional polymer is an elastomer.
 20. Thetherapeutic-agent-releasing medical device of claim 1, wherein saidadditional polymer is blended with said styrene copolymer in the releaselayer.
 21. The therapeutic-agent-releasing medical device of claim 20,wherein the additional polymer is a copolymer comprising (a) one or moreblocks of polyisobutylene and (b) one or more blocks of polystyrene orpoly-alpha-methylstyrene.
 22. The therapeutic-agent-releasing medicaldevice of claim 20, wherein the additional polymer is a copolymercomprising (a) one or more blocks of polystyrene and (b) one or morepolymer blocks of ethylene and butylene.
 23. Thetherapeutic-agent-releasing medical device of claim 20, wherein theadditional polymer is a poly(butyl methacrylate).
 24. Thetherapeutic-agent-releasing medical device of claim 1, wherein saidadditional polymer is crosslinked with said styrene copolymer in therelease layer.
 25. The therapeutic-agent-releasing medical device ofclaim 1, wherein said styrene copolymer is a copolymer comprising (a) amonomer selected from acrylonitrile, maleic anhydride, and a maleicanhydride derivative and (b) a styrene monomer, wherein said additionalpolymer is blended with said styrene copolymer in the release layer, andwherein said additional polymer is a copolymer comprising (a) one ormore blocks selected from blocks of polyisobutylene and blocks ofethylene and butylene and (b) one or more blocks selected from blocks ofpolystyrene or blocks of poly-alpha-methylstyrene.
 26. Thetherapeutic-agent-releasing medical device of claim 1, wherein saidrelease layer is formed by a solvent-based technique in which saidstyrene copolymer and said additional polymer are dissolved or dispersedin a solvent which is applied to all or a portion of said implantable orinsertable medical devices.
 27. The therapeutic-agent-releasing medicaldevice of claim 26, wherein said solution is applied to all of saidimplantable or insertable medical device.
 28. Thetherapeutic-agent-releasing medical device of claim 1, wherein less than25% of the total release from the medical device that occurs over thecourse of implantation/insertion in the body occurs within the first 3days of administration.